1. Field of the Invention
The present invention relates to a liquid crystal display device and related method, and more particularly, to a liquid crystal display device and method for decaying residual image of the liquid crystal display device.
2. Description of the Prior Art
Because liquid crystal display (LCD) devices are characterized by thin appearance, low power consumption, and low radiation, LCD devices have been widely applied in various electronic products such as computer monitors, mobile phones, personal digital assistants (PDAs), or flat panel televisions. In general, the LCD device comprises liquid crystal layers encapsulated by two substrates. By means of varying voltage drops between opposite sides of the liquid crystal layers, the twisted angles of the liquid crystal molecules of the liquid crystal layers can be changed so that the transparency of the liquid crystal layers can also be changed accordingly for illustrating images.
FIG. 1 is a diagram schematically showing the structure of a prior-art thin film transistor liquid crystal display (TFT-LCD) device. As shown in FIG. 1, the TFT-LCD device 10 comprises a liquid crystal display panel 100, a power circuit 150, a source driving circuit 104, a gate driving circuit 106, and a voltage generator 108. As aforementioned, the liquid crystal display panel 100 normally comprises two substrates and liquid crystal layers being stuffed between the substrates. One of the substrates is disposed with a plurality of data lines 110, a plurality of gate lines (or scan lines) 112 perpendicular to the data lines 110, and a plurality of thin film transistors (TFTs) 114. The other one of the substrates is disposed with a common electrode for receiving a common voltage Vcom provided by the voltage generator 108. For the sake of elucidation, FIG. 1 reveals only four thin film transistors 114, but in a real case, there is one thin film transistor 114 disposed at each intersection of a data line 110 and a gate line 112 on the LCD panel 100. That is, the plurality of thin film transistors 114, each corresponding to a pixel of the TFT-LCD device 10, form a matrix on the LCD panel 100, and the data lines 110 and the gate lines 112 are corresponding to columns and rows of the matrix. In addition, an equivalent circuit resulted from the two substrates of the LCD panel 100 can be regarded as a plurality of equivalent capacitors 116. Each of the plurality of equivalent capacitors 116 comprises at least a liquid crystal capacitor and at least a storage capacitor, and functions to act as a storage unit.
The power circuit 150 comprises a plurality of level shifters 151, 152, and 153 for converting a vertical start logic signal STV, a first clock logic signal CLK1L, and a second clock logic signal CLK2L into a vertical start signal ST, a first clock signal CLK1, and a second clock signal CLK2 respectively. The vertical start signal ST, the first clock signal CLK1, and the second clock signal CLK2 are furnished to the gate driving circuit 106. Besides, the power circuit 150 transfers a low-level gate signal reference voltage Vgl to the gate driving circuit 106.
The operation principle for driving the prior-art TFT-LCD device 10 is briefed as the following. When the power circuit 150 receives the vertical start logic signal STV, the first clock logic signal CLK1L, and the second clock logic signal CLK2L, the high/low logic levels of the signals STV, CLK1L, and CLK2L are converted to the high-level/low-level gate signal reference voltages by the power circuit 150 so as to generate the vertical start signal ST, the first clock signal CLK1, and the second clock signal CLK2 forwarded to the gate driving circuit 106. Thereafter, the gate driving circuit 106 and the source driving circuit 104 are able to generate gate signals and data signals furnished to the corresponding gate lines 112 and data lines 110 for controlling the operations of the thin film transistors 114 and the voltage drops across the equivalent capacitors 116. The twisted angles of liquid crystal molecules corresponding to the equivalent capacitors 116 are then changed in response to the voltage drops, and hence the corresponding transparency of the liquid crystal layers can be changed accordingly for illustrating images.
For instance, when the gate driving circuit 106 forwards a gate signal to a gate line 112 for turning on corresponding thin film transistors 114, the data signals forwarded to the data lines 110 by the source driving circuit 104 can be furnished to the corresponding equivalent capacitors 116 via the corresponding thin film transistors 114 being turned on. Consequently, the gray levels of corresponding pixels can be controlled based on the data signals.
However, upon turning off the TFT-LCD device 10, the electric charges accumulated in the equivalent capacitors 116 cannot be discharged rapidly and can only be released through the leakage currents of the thin film transistors 114, which is a time-consuming discharging process. That is, the displayed image cannot vanish immediately after power-off and will persist for a relatively long time, which is known as the residual image effect. The residual image displayed on the TFT-LCD device 10 may cause an unpleasant visual experience.